Hot air generator device with improved lighting

ABSTRACT

A hot air generating device of the type including an injection device ( 2 ) capable of producing a flow of a combustible gas mixture at a high speed and a burner head ( 3 ) in which the flow is ignited via a spark plug ( 6 ) positioned near the burner ( 3 ) and electrically connected to a lighter ( 12 ), preferably a piezoelectric lighter, including an autotransformer mounted in parallel between the lighter and the spark plug. Such a device is particularly advantageous to facilitate the lighting of the mixture, in particular when the device is provided with a riser between the lighter and the spark plug.

The present invention relates to a burner/hot air generator device with a riser usable, in particular but not exclusively, for low-temperature heating of a plastic film, for example a polyethylene film for the retraction thereof using a gas flow coming from the combustion of a combustible gas such as propane or air or to place thermoplastic material on the ground.

The invention more particularly relates to a burner of the type previously described equipped with a riser consisting of a generally tubular element, potentially telescoping, able to insert itself between the injection device and the burner head, of the device.

Such a device is in particular described in patent FR 2 907 882.

One problem results from the fact that the riser is made from an electrically conductive material and is connected to the ground of the electric generator (piezoelectric). As a result, the conductor, which passes into the riser to connect the outlet of the electric generator to a lighting electrode (spark plug) arranged in the lighting chamber of the burner, constitutes, with the riser, a capacitor whereof the capacity depends on the length of the riser and the arrangement of the conductor inside said riser. This capacitor has the drawback of absorbing a significant fraction of the electric charge delivered by the electric generator at the time of the lighting. The charge applied to the spark plug is therefore weakened. To increase the voltage at the terminals of the spark plug, the manufacturer is led to increase the shock on the lighter and/or the operator is led to strike the lighter several times, which considerably reduces its lifetime.

The invention more particularly aims to eliminate these drawbacks. Furthermore, the invention must in particular have a reduced weight and bulk, so as to preserve the portability of the device, and to allow it to be used during long working periods.

To that end, the invention proposes a hot air generating device of the type comprising an injection device capable of producing a flow of a combustible gas mixture at a high speed and a burner head in which the flow is ignited via a spark plug positioned in said burner and electrically connected to a lighter, preferably a piezoelectric lighter, said device also comprising means to reduce the capacitive losses between the lighter and the spark plug.

This device also may or may not comprise a riser tube between the injection device and the burner.

The means for reducing losses comprise means to make the increase in the voltage at the terminals of the spark plug more gradual; in particular, they can be a transformer, of the autotransformer type, mounted in parallel with the lighter.

Preferably, the transformer is mounted as a step-down transformer. A piezoelectric lighter can easily produce a voltage peak of 14 kV, or even 20 kV, whereas a voltage of 8 kV is generally sufficient at the terminals of the spark plug to ignite the gaseous mixture.

Advantageously, the transformer is mounted near the lighter. In particular, if the device comprises a riser tube, the transformer is preferably mounted at one end of the tube opposite the burner.

Several embodiments of the invention are described hereafter, as non-limiting examples, in reference to the appended figures, in which:

FIG. 1 is a view of a hot air generating device, supported by an operator; and

FIG. 2 is an electric diagram of a lighting circuit according to the invention, adapted in particular to equip the device of FIG. 1.

In the example shown in FIG. 1, the device 1 comprises an injection device, in the form of a gun 2, able to transmit a flow of combustible gaseous mixture to the head of the burner 3. The gun 2 and the burner 3 are connected to each other by a riser tube 4. The tube 4 is generally made from aluminum, in particular to limit the weight thereof. In certain device models, such a tube 4 can make it possible to offset the burner 3 at a distance of about two meters from the gun 2.

FIG. 2 illustrates an electric diagram for a device according to the invention. The brackets are arranged to indicate in what zone of the device (gun 2, tube 4 or burner 3) the corresponding part of the diagram is situated.

In the illustrated example, the device 1 comprises a spark plug 6, arranged in the burner, to make it possible to ignite the gaseous mixture. The spark plug 6 is supplied with a voltage generated by a piezoelectric lighter 7 arranged in the body of the gun 2. An electric connection between the lighter 7 and the spark plug 6 is ensured on the one hand by the riser tube 4, connected to the ground of the lighter 7, and on the other hand by a linear conductor 8, kept at a distance inside the tube 4.

According to the invention, a transformer 9, of the autotransformer type, is mounted in parallel with the lighter 7. In the example illustrated in FIG. 2, the transformer 9 is used in a step-down transformer version, so that the voltage T6 at the terminals of the spark plug 6 is lower than the voltage T7 produced by the lighter 7. Thus, the voltage step-down can be such that the ratio T6/T7 of the voltages is 2/3, or even 3/4; advantageously, this ratio can be provided to be reversible, for example 3/2 or 4/3.

It will be noted that in the usage made thereof, the transformer has not been provided to operate at a constant rating, but rather only according to a regular pulse rating, upon each ignition. The transformer is advantageously calculated so as to include an equivalent “parallel” capacity sufficient to make the voltage “creep,” i.e. to make the increase of the voltage T6 more gradual at the terminals of the spark plug 6, so as to reduce the capacitive losses, in particular between the conductor 8 and the tube 4. For better effectiveness, the transformer is mounted in the gun 2, as close as possible to the lighter 7.

Of course, the invention is not limited to the preferred embodiments just described, but on the contrary is defined by the claims that follow.

One skilled in the art will in fact see that various modifications can be made to the embodiments described above, in light of the teaching just disclosed.

Thus, the transformer can be mounted in a step-up voltage version. 

1. A hot air generating device of the type comprising an injection device (2) capable of producing a flow of a combustible gas mixture at a high speed and a burner head (3) in which the flow is ignited via a spark plug (6) positioned near said burner (3) and electrically connected to a lighter (7), preferably a piezoelectric lighter, characterized in that it also comprises means (9) to reduce the capacitive losses between the lighter and the spark plug.
 2. The device according to claim 1, characterized in that it comprises a riser tube between the injection device (2) and the burner (3).
 3. The device according to claim 1, characterized in that the means (9) for reducing losses comprise means to make the increase in the voltage (T6) at the terminals of the spark plug (6) more gradual.
 4. The device according to claim 3, characterized in that the means (9) for reducing losses comprise a transformer (9), of the autotransformer type, mounted in parallel with the lighter (7).
 5. The device according to claim 4, characterized in that the transformer (9) is mounted as a step-down transformer.
 6. The device according to claim 4, characterized in that the transformer (9) is mounted near the lighter (7).
 7. The device according to claim 2, characterized in that the means (9) for reducing losses comprise means to make the increase in the voltage (T6) at the terminals of the spark plug (6) more gradual.
 8. The device according to claim 7, characterized in that the means (9) for reducing losses comprise a transformer (9), of the autotransformer type, mounted in parallel with the lighter (7).
 9. The device according to claim 8, characterized in that the transformer (9) is mounted as a step-down transformer.
 10. The device according to claim 5, characterized in that the transformer (9) is mounted near the lighter (7).
 11. The device according to claim 10, characterized in that the transformer (9) is mounted near the lighter (7). 